The Nikkei share average was up 0.2 percent at 22,191.48 in midmorning trade. It dipped briefly into negative territory after soaring 1.1 percent to a two-week high.

The polls in more than half the 50 U.S. states closed during Asian morning trade after a divisive election campaign that will shape the future of Donald Trump's presidency.

Most of the key races that will decide control of the U.S. Congress were still too close to call.

The opposition Democrats are favoured by election forecasters to pick up the first of the 23 seats to gain a House majority.

"The market has almost priced-in the possibility of a split Congress, so if this becomes the result, the market will likely rise in relief," said Norihiro Fujito, a chief investment strategist at Mitsubishi UFJ Morgan Stanley Securities, adding that stock investors would cheer U.S. President Donald Trump's policy to push for corporate growth.

"If Republicans get both houses of Congress, some people may be reminded of a Trump rally that they experienced two years ago and the market may rise sharply," Fujito said.

Telecom giant NTT Corp jumped 6 percent to 4,541 yen after the company said it would buy back up to 150 billion of its own shares.

It also announced a mid-term business plan in which it aims for earnings per share of 640 yen for the fiscal year ending March 2024, 50 percent more than the 425 yen posted in the fiscal year ended March 2018.

Olympus Corp tumbled 5 percent after it cut its net profit outlook for the year through March to 26 billion yen from 40 billion yen.

Mitsubishi Materials nosedived 10 percent after it cut its net profit forecast to 25 billion yen from 35 billion yen for the year ending March.